A recently developed type of secondary battery or rechargeable electrical conversion device comprises: (A) an anodic reaction zone containing a molten alkali metal reactant-anode, e.g., sodium, in electrical contact with an external circuit; (B) a cathodic reaction zone containing (a) a cathodic reactant comprising a liquid electrolyte, e.g., sulfur or a mixture of sulfur and molten polysulfide, which is electro-chemically reversibly reactive with said anodic reactant and (b) a porous felt electrode prepared from a material selected from metal, carbon and graphite; (C) a solid electrolyte comprising a cation-permeable barrier to mass liquid transfer interposed between and in contact with said anodic and cathodic reaction zones; and (D) a current collector or backup electrode. The felt electrode is in electrical contact with the cation-permeable barrier and also in electrical contact with the current collector or backup electrode which, in turn, is in electrical contact with the external circuit.
As used herein, the term "reactant" is intended to mean reactants and reaction products.
In a battery or cell of the above type the current collector or backup electrode and the porous cathodic electrode must make good contact in order to complete the electrical circuit. Generally, this may be accomplished by bonding the electrode and the current collector such as with a conductive cement. In prior art devices, the current collector or backup electrode has been prepared from conductive material such as graphite or various metals. However, the metals as well as the graphite are subject to some corrosion or build up of corrosion products and the bond between the current collector/backup electrode and the felt has been subject to failure due to degradation of the bonding cement. Both of these problems have resulted in a cell or battery of diminished capacity.
It is an object of this invention to prepare a composite body in which a current collector or backup electrode is integrally bonded to a cathodic felt electrode in such a manner that the composite does not suffer from the above corrosion problems or failure of a bonding medium.
Thus, it is a primary object of this invention to prepare such a secondary battery or cell of increased capacity compared to batteries or cells in which a felt electrode is bonded by a bonding cement to a corrodible or porous current collector subject to buildup of corrosion products.